As a typical example of the surface defect inspection of the above-noted type, there can be cited a technique employed for inspection of a painted surface of an automobile body (specifically, its bumper). The inspection target of such surface defect inspection is e.g. unevenness, a scar, etc. present on the painted surface as the inspection target surface.
As an inspection technique using an irradiation light which forms a pattern on the irradiated surface, there is known a technique including the steps of irradiating the painted surface with an irradiation light forming the so-called stripe-like, i.e. horizontal-stripes like lightness/darkness, imaging the irradiated painted surface by an imaging camera and inspecting the surface by using the obtained image.
A specific construction of such inspection system is shown in FIG. 17.
In this defect inspection system shown in FIG. 17, a charging worker 204 takes out a bumper 1, when needed, from a stock station 202 where a plurality of bumpers as inspection targets are stocked, and sets it to a robot 22 which can change its posture, with holding the bumper 1.
The robot 22, while holding the bumper 1, changes the posture of the bumper 1 by rotating it about a rotational axis 22d shown in FIG. 17. The system includes an irradiation apparatus 220 operable to irradiate an irradiation light with a predetermined horizontal-stripe pattern, in association with the above change in the posture. In the illustrated example, this apparatus 220 is disposed so as to surround a moving space within which the posture of the bumper 1 is changed. The irradiation pattern of the irradiation light is a stripe-like lightness/darkness pattern parallel with the rotational axis 22d of the bumper 1.
At predetermined positions of the irradiation apparatus 220, there are provided a plurality of imaging cameras 4. With these cameras 4, the images of the lightness/darkness pattern of the irradiation light reflected off the bumper 1 are obtained. The results of these imaging operations are sent to an analyzing section where evaluation of presence/absence of a defect is carried out.
Upon completion of the above-described retention/posture change by the robot 22, an inspecting worker 201 positioned downstream of the robot 22 removes the bumper 1 from the robot and forwards this to a subsequent process such as a visual inspection.
At the time described above, the inspecting worker 201 has obtained evaluation information from defect evaluating means. Hence, as the worker has already obtained information needing attention in the inspection, the worker can proceed in the process speedily and reliably.
FIG. 18 illustrates the basic principle of the surface defect inspection of the above-described construction.
As shown in this figure, as the painted surface is moved along a predetermined direction (e.g. the direction R), an image portion of a defect such as unevenness on the painted surface is imaged while varying the coordinate of that direction (R coordinate) without changing the coordinate in the direction (e.g. the direction of the two sides of the plane of FIG. 18) normal to the moving direction R. With this, the defect can be detected.
That is, the defect is discriminated by utilizing the fact that the defect area will appear dark in a light stripe portion or will appear light in a dark stripe portion in the obtained image. Hence, the defect can be recognized as an intermediate gradation image in the light portion or the dark portion in the stripes. A technique utilizing a similar inspection principle is disclosed in Patent Document 1.
Further, for the purpose of detecting a defect called “orange peel” which is periodical unevenness in the surface, there is known a technique of detecting non-uniformity in the paint thickness through fluctuation of a lightness/darkness stripes as an irradiation light at a border line in the obtained image (see Patent Document 2).
With this inspection method, there is no need for moving the inspection target surface. However, this method is directed mainly for such a painted surface having a disturbance which causes a displacement of the border line image of the stripes over a relatively large area in the painted surface.
Patent Document 1: Japanese Patent Application “Kokai” No. 8-145906 (FIGS. 5, 9 and 15).
Patent Document 2: Japanese Patent Application “Kokai” No. 9-126744 (FIG. 13).